Abstract

BACKGROUND:

Most currently approved anti-HIV drugs (e.g., reverse transcriptase inhibitors, protease inhibitors and fusion/entry inhibitors) must act inside or on surface of the target cell to inhibit HIV infection, but none can directly inactivate virions away from cells. Although soluble CD4 (sCD4) can inactivate laboratory-adapted HIV-1 strains, it fails to reduce the viral loads in clinical trials because of its low potency against primary isolates and tendency to enhance HIV-1 infection at low concentration. Thus, it is essential to design a better HIV inactivator with improved potency for developing new anti-HIV therapeutics that can actively attack the virus in the circulation before it attaches to and enter into the target cell.

RESULTS:

We engineered a bivalent HIV-1 inactivator, designated 2DLT, by linking the D1D2 domain of CD4 to T1144, the next generation HIV fusion inhibitor, with a 35-mer linker. The D1D2 domain in this soluble 2DLT protein could bind to the CD4-binding site and induce the formation of the gp41 prehairpin fusion-intermediate (PFI), but showed no sCD4-mediated enhancement of HIV-1 infection. The T1144 domain in 2DLT then bound to the exposed PFI, resulting in rapid inactivation of HIV-1 virions in the absence of the target cell. Beside, 2DLT could also inhibit fusion of the virus with the target cell if the virion escapes the first attack of 2DLT.

CONCLUSION:

This bivalent molecule can serve as a dual barrier against HIV infection by first inactivating HIV-1 virions away from cells and then blocking HIV-1 entry on the target cell surface, indicating its potential for development as a new class of anti-HIV drug.

“Now a team led by Shibo Jiang has designed a novel bi-specific inhibitor, 2DLT, which essentially is a fusion protein of a soluble version of CD4 and the third generation fusion inhibitor T1144”. “The beauty of the 2DLT inhibitor is not its dual activity per se, but its potential to inactivate the virus in the absence of cells.” “The CD4 component of 2DLT also induces the short-lived activated Env form, but then the fusion inhibitor component, T1144, delivers a second blow by binding and blocking the activated fusion machinery in gp41. Thus, 2DLT induces a premature and irreversible collapse of the viral mousetrap, thereby preventing viral entry into target cells.” “2DLT may be considered for use as a microbicide – for example, in vaginal gels that are aimed at preventing HIV-1 transmission at the vaginal mucosal surface. Another interesting application of 2DLT could be in viral immune prophylaxis (VIP), a gene therapy vaccination approach”. “In summary, the bi-specific and dual active 2DLT inhibitor described by Lu et al., with its one-two punch that inactivates free virus, represents a novel drug approach that warrants further evaluation.”

A double hit against HIV. Unlike the traditional antiretroviral drugs that must passively wait inside the host cell to inhibit HIV replication, 2DLT can actively attack the HIV outside the cell via a two-punch mechanism, i.e., the D1D2 domain in 2DLT first hits gp120 to expose the gp41 fusion-intermediate, which is then attacked by the T1144 domain in 2DLT, resulting in irreversible inactivation of HIV.